The aim of the proposed research is to investigate certain aspects of the control of gene expression in mammalian and other eukaryotic cells. We propose to extend our studies of the role of nuclear ribonucleoprotein complexes in the processing of nuclear RNA and the transport of messenger-RNA from nucleus to cytoplasm. We intend to study the function of these complexes in normal resting and stimulated tissues (regenerating liver, for example) and in neoplastic cells. The possible involvement of the proteins of the complex in post-transcriptional modulation of gene expression will be assessed. We have previously purified the 30S ribonucleoprotein complex of mouse ascites tumor cells, which contains the bulk of the heterogeneous nuclear RNA, and we intend to isolate a smaller complex (ca 15S) which, we have found, contains polyadenylate sequences (poly A) in these tumor cells. Analysis of the purified particles will provide the techniques for study of their role in vivo living cell. In particular, any similarities between the nuclear species and cytoplasmic messenger RNA-containing complexes will be determined by both chemical and immunological means. The nature of the RNA-protein interaction in 30S complexes will be examined in greater detail, in order to understand our observation of the preferred binding of heterogeneous nuclear and messenger RNAs, compared with ribosomal and transfer RNA molecules. In addition, the fine structure of purified complexes will be studied, and an attempt made to determine the intra-nuclear site of these structures.